#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<assert.h>
#include<stdio.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<fcntl.h>
#include<stdlib.h>
#include<poll.h>

#define _GNU_SOURCE 1

#define USER_LIMIT  5
#define BUFFER_SIZE 64
#define FD_LIMIT    65535

#define POLLRDHUP   0x2000

struct client_data{
    struct sockaddr_in address;
    char *write_buf;
    char buf[BUFFER_SIZE];
};
int setnonblocking(int fd){
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

int main(int argc, char *argv[]){
    if(argc <= 2){
        printf("usage: %s ip_address port_number\n", argv[0]);
        return 1;
    }

    const char *ip = argv[1];
    int port = atoi(argv[2]);
    int i;
    int j;

    int ret = 0;
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

    int listenfd = socket(PF_INET, SOCK_STREAM, 0);
    assert(listenfd >= 0);

    ret = bind(listenfd, (struct sockaddr *)&address, sizeof(address));
    assert(ret != -1);

    ret = listen(listenfd, 5);
    assert(ret != -1);

    struct client_data *users = (struct client_data *)malloc(sizeof(struct client_data) * FD_LIMIT);

    struct pollfd fds[USER_LIMIT+1];
    int user_counter = 0;
    for(i = 0; i < USER_LIMIT; i++){
        fds[i].fd = -1;
        fds[i].events = 0;
    }

    fds[0].fd = listenfd;
    fds[0].events = POLLIN | POLLERR;
    fds[0].revents = 0;

    while(1){
        ret = poll(fds, user_counter+1, -1);
        if(ret < 0){
            printf("poll failure\n");
            break;
        }

        for(i = 0; i < user_counter+1; i++){
            if((fds[i].fd == listenfd) && (fds[i].revents & POLLIN)){
                struct sockaddr_in client_address;
                socklen_t client_addrlength = sizeof(client_address);
                int connfd = accept(listenfd, (struct sockaddr *)&client_address, &client_addrlength);
                if(connfd < 0){
                    printf("errno is: %d\n", errno);
                    continue;
                }

                if(user_counter >= USER_LIMIT){
                    const char *info = "too many users\n";
                    printf("%s", info);
                    send(connfd, info, strlen(info), 0);
                    close(connfd);
                    continue;
                }
                user_counter++;
                users[connfd].address = client_address;
                setnonblocking(connfd);
                fds[user_counter].fd = connfd;
                fds[user_counter].events = POLLIN | POLLRDHUP | POLLERR;
                fds[user_counter].revents = 0;
                printf("comes a new user, now have %d users\n", user_counter);
            }else if(fds[i].revents & POLLERR){
                printf("get an error from %d\n", fds[i].fd);
                char errors[100];
                memset(errors, '\0', 100);
                socklen_t length = sizeof(errors);
                if(getsockopt(fds[i].fd, SOL_SOCKET, SO_ERROR, &errors, &length) < 0){
                    printf("get socket option failed\n");
                }
                continue;
            }else if(fds[i].revents & POLLRDHUP){
                users[fds[i].fd] = users[fds[user_counter].fd];
                close(fds[i].fd);
                fds[i] = fds[user_counter];
                i--;
                user_counter--;
                printf("a client left\n");
            }else if(fds[i].revents & POLLIN){
                int connfd = fds[i].fd;
                memset(users[connfd].buf, '\0', BUFFER_SIZE);
                ret = recv(connfd, users[connfd].buf, BUFFER_SIZE-1, 0);
                printf("get %d bytes of client data %s from %d\n", ret, users[connfd].buf, connfd);
                if(ret < 0){
                    if(errno != EAGAIN){
                        close(connfd);
                        users[fds[i].fd] = users[fds[user_counter].fd];
                        i--;
                        user_counter--;
                    }
                }else if(ret == 0){

                }else{
                    for(j = 1; j < user_counter; j++){
                        if(fds[j].fd == connfd){
                            continue;
                        }
                        fds[j].events |= ~POLLIN;
                        fds[j].events |= POLLOUT;
                        users[fds[j].fd].write_buf = users[connfd].buf;
                    }
                }
            }else if(fds[i].revents & POLLOUT){
                int connfd = fds[i].fd;
                if(!users[connfd].write_buf){
                    continue;
                }

                ret = send(connfd, users[connfd].write_buf, strlen(users[connfd].write_buf), 0);
                users[connfd].write_buf = NULL;
                fds[i].events |= ~POLLOUT;
                fds[i].events |= POLLIN;
            }

        }
    }

    free(users);
    close(listenfd);
    return 0;
}
